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Geologic map
Age of Oceanic crust: Important note: These geologic province map depicts only features approximately 150 km across and greater due to the fact that the resolution of the maps should be consistent with the resolution of the seismic refraction data. For example, the young uplifted blocks of the Variscan Orogen in Central and Western Europe such as the Rhenish Massif or the Massif Central are not depicted as ‘orogens’ but as part of the ‘extended continental crust’ in the western half of Europe.}} |Source=http://earthquake.usgs.gov/data/crust/maps.php |Date=original upload english wikipedia 22 April 2005 by SEWilco |Author=USGS |Permission= |other_versions= World geologic provinces North America cropped.png }} }} A geologic map or geological map is a special-purpose map made to show geological features. Rock units or geologic strata are shown by color or symbols to indicate where they are exposed at the surface. Bedding planes and structural features such as faults, folds, foliations, and lineations are shown with strike and dip or trend and plunge symbols which give these features' three-dimensional orientations. Stratigraphic contour lines may be used to illustrate the surface of a selected stratum illustrating the subsurface topographic trends of the strata. Isopach maps detail the variations in thickness of stratigraphic units. It is not always possible to properly show this when the strata are extremely fractured, mixed, in some discontinuities, or where they are otherwise disturbed. Lithologies Rock units are typically represented by colors. Instead of (or in addition to) colors, certain symbols can be used. Different geologic mapping agencies and authorities have different standards for the colors and symbols to be used for rocks of differing types and ages. Orientations take two major types of orientation measurements (using a like a ): orientations of planes and orientations of lines. Orientations of planes are often measured as a "strike" and "dip", while orientations of lines are often measured as a "trend" and "plunge". Strike and dip symbols consist of a long "strike" line, which is perpendicular to the direction of greatest slope along the surface of the bed, and a shorter "dip" line on side of the strike line where the bed is going downwards. The angle that the bed makes with the horizontal, along the dip direction, is written next to the dip line. In the azimuthal system, strike and dip are often given as "strike/dip" (for example: 270/15, for a strike of west and a dip of 15 degrees below the horizontal). Trend and plunge are used for linear features, and their symbol is a single arrow on the map. The arrow is oriented in the downgoing direction of the linear feature (the "trend") and at the end of the arrow, the number of degrees that the feature lies below the horizontal (the "plunge") is noted. Trend and plunge are often notated as PLUNGE → TREND (for example: 34 → 86 indicates a feature that is angled at 34 degrees below the horizontal at an angle that is just East of true South). Footnotes External links * IGME 5000 International Geological Map of Europe and Adjacent Areas 1:5.000.000, Asch, K (2005), Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), Hannover * Geology of Britain viewer from the British Geological Survey, at 1:50,000 and 1:625,000 scales * Geologic Maps from USGS National Park Service * USGS National Geologic Map Database * Maclure's 1809 Geological Map of the United States Category:Geology Category:Geomorphology Category:Stratigraphy